I remember a message about the 'E' marked barrels a while back, not sure of the manufacturer but there was a batch of them shipped to the Army that had unpolished and scratched chambers. It was not a mandatory changeout if you had an ‘E’ marked barrel, just a recurring inspection.
If the weapon had problems with stuck/ruptured cartridges you could change the barrel even if new because of the scratched chambers.
We had one Reserve unit that was getting ready to deploy to Iraq and the Commander wanted all of his barrels changed. We tried to tell him that the message was not a mandatory change out but he didn’t want to hear it. He got his way, and we had to change out 135 barrels in less than a week. Overtime paid!
I just can’t remember the manufacturer anymore, although I am sure someone here can supply the info.